Distinct classes of phosphatidylinositol 3 '-kinases are involved in signaling pathways that control macroautophagy in HT-29 cells

3-Methyladenine which stops macroautophagy at the sequestration step in mam malian cells also inhibits the phosphoinositide 3-kinase (PI3K) activity ra ising the possibility that PI3K signaling controls the macroautophagic path way (Blommaart, E. F. C., Krause, U., Schellens, J. P. M., Vreeling-Sindela rova, H., and Meijer, A. J. (1997) fur. J, Biochem. 243, 240-246). The aim of this study was to identify PI3Ks involved in the control of macroautopha gic sequestration in human colon cancer HT-29 cells. An increase of class I PISK products (phosphatidylinositol 3,4-bisphosphate and phosphatidylinosi tol 3,4,5-triphosphate) caused by either feeding cells with synthetic lipid s (dipalmitoyl phosphatidylinositol 3,4-bisphosphate and dipalmitoyl phosph atidylinositol 3,4,5-triphosphate) or by stimulating the enzymatic activity by interleukin-13 reduced macroautophagy, In contrast, an increase in the class III PISK product (phosphatidylinositol 3-phosphate), either by feedin g cells with a synthetic lipid or by overexpressing the p150 adaptor, stimu lates macroautophagy. Transfection of a specific class III PISK antisense o ligonucleotide greatly inhibited the rate of macroautophagy. In accordance with a role of class III PISK, wortmannin tan inhibitor of PI3Ks) inhibits macroautophagic sequestration and protein degradation in the low nanomolar range (IC50 5-15 nM), Further in vitro enzymatic assay showed that 3-methyl adenine inhibits the class III PISK activity. Dipalmitoyl phosphatidylinosi tol 3-phosphate supplementation or p150 overexpression rescued the macroaut ophagic pathway in HT-29 cells overexpressing a GTPase-deficient mutant of the G alpha(i3) protein suggesting that both class III PISK and trimeric G( i3) protein signaling are required in the control macroautophagy in HT-29 c ells. In conclusion, our results demonstrate that distinct classes of PI3K control the macroautophagic pathway in opposite directions. The roles of PI 3Ks in macroautophagy are discussed in the context of membrane recycling.